The present invention relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a well tool having an enhanced performance packing element assembly.
Many well tools use packing element assemblies to seal off an annular space. Examples of such well tools include packers, tubing and liner hangers, etc.
Typical packing element assemblies include multiple packing elements, backup rings and other elements, such as packing element separators. Each of these structures has a useful function to perform in the overall assembly, but experience shows that well fluid can become trapped between the structures when the packing element assembly is expanded radially outward to seal off the annular space.
Attempts have been made in the past to alleviate this problem of trapped fluid in packing element assemblies. One proposed solution is to increase the setting force used to expand the assembly. However, increased setting force requires larger setting pistons, application of increased pressure and/or components having increased strength, etc. Each of these presents its own set of problems to overcome.
Another proposed solution is to increase the time period during which the packing element assembly is expanded. In this manner, more time is allowed for the fluid to escape from the packing element assembly. However, increasing the setting time requires pressure to be applied for a longer period and/or increases the cost of the setting operation, etc.
Yet another proposed solution is to provide fluid escape routes in the form of holes or slots in the backup rings. However, this leads to undesirable stress concentrations in the backup rings and/or allows excess extrusion of packing elements through the holes or slots, etc.
Therefore, it may be seen that improvements are needed in the art of packing element assembly construction.